1. Field of the Invention
The present invention relates to portable electronic instruments and devices having an active or normal operating mode and an inactive, waiting or standby state or mode in which only basic functions are operational; it relates more particularly to radio communication devices, in particular cellular radio communication devices.
The invention provides an integrated circuit for use in a device of the type previously cited having a standby mode characterized by very low power consumption and a portable or mobile radio communication device including that kind of integrated circuit.
2. Description of the Prior Art
An essential parameter and constant concern for designers and manufacturers of portable instruments or devices incorporating their own electrical power supply is reducing their electrical power consumption and thereby improving their autonomy (the duration of operation before replacing or recharging the battery).
Given that constraint, manufacturers of such devices soon defined, in addition to ON and OFF states, a “standby” mode of operation corresponding to a reduced mode of operation in the ON state in which power consumption is low and only a few essential basic functions are active (internal clocks, active registers, etc.).
This applies to devices including telecommunication devices, and in particular to mobile or cellular telephones.
For example, a digital baseband dedicated circuit basic function (the 32 kHz module) is always active in a GSM (Global System for Mobile communications) or UMTS (Universal Mobile Telecommunication System), also known as a third generation terminal, which is in the ON state.
The 32 kHz module mainly consists of an oscillator, registers and counters, and remains on and active in the ON/standby (low power consumption) state or mode of operation. It maintains the GSM time locally when the main oscillator of the voltage-controlled device is off and no radio link is set up. It also “wakes up” the terminal, i.e. commands its return to the active mode after each period on standby.
The 32 kHz module is at present integrated into the baseband dedicated circuit and it is therefore necessary for that circuit to be on even during periods in which the terminal is in the standby mode.
Although it represents a penalty, this powering of a complete circuit of which only one particular function is effectively active can at present be accepted since the static leakage per transistor is of the order of picoamperes/micron.
The baseband dedicated circuit generally integrates less than 10 million transistors and the overall static leakage current for the whole of the integrated circuit is therefore less than 100 microamperes. These values correspond to CMOS transistors of up to 0.25 micron, or possibly up to 0.18 micron with special arrangements.
However, new generation CMOS integrated circuits, with etching or track widths of the order of 0.10 micron, have a static leakage of approximately 20 nanoamperes/micron (see in particular “International Technology Roadmap for Semiconductors”, 1999, SEMATECH). The resulting overall static leakage for the whole of the GSM baseband circuit could achieve values of the order of 100 milliampere, which would be greater than the power consumption in the active mode and during a call.
To attempt to overcome the aforementioned drawbacks, it has been proposed, in particular in the document EP-A-0 939 495, to remove the 32 kHz module from the digital baseband dedicated circuit and implement it as a separate component distinct from the aforementioned dedicated circuit or to integrate it into another dedicated circuit of smaller size, such as the power supply management circuit.
This separates off the “GSM time” function and partially implements it in two separate circuits, namely the power supply management circuit and the digital baseband circuit, and therefore leads to a new design of the architecture of the two circuits.
This necessarily results in exchanges of information between the two circuits, in particular to update or resynchronize the GSM time; these exchanges of information are relatively difficult to manage.
One object of the present invention is to propose a solution that significantly reduces the power consumption during periods in which the terminal is in the inactive or standby mode but avoids the drawbacks of the solution previously cited.